Resilient Modulus Testing on Indiana Subgrade Soils (05-1609)**
Daehyeon Kim, Chosun University, South Korea
Nayyar Zia Siddiki, Indiana Department of Transportation

ABSTRACT Resilient modulus has been used for characterizing stress-strain behavior of subgrades in the design of pavements. Recently the Resilient modulus (Mr) testing procedure has been upgraded through AASHTO T 307. Since the testing procedure is still complex, the testing has not been widely implemented in practice. In this study, the applicability of a simplified procedure with a confining pressure of 2 psi and deviator stresses of 2, 4, 6, 8, 10, and 15 psi was investigated on the typical coarse-grained and fine-grained subgrade soils encountered in Indiana. The results obtained from the simplified procedure are comparable with those obtained from AASHTO T 307 which calls for 15 combinations of stresses. This shows the simplified procedure to be feasible and effective for design purpose. For soils exhibiting excessive permanent deformation, use of deformed length is desirable for more accurate calculation of Mr. Usually the soils compacted dry of optimum shows the largest Mr for coarse-grained soils due to capillary suction, but it not necessary true for fine-grained soils. A predictive model to estimate regression coefficients k1, k2, and k3 using 11 soil variables obtained from the soil property tests and the Standard Proctor tests was developed. The predicted regression coefficient compares well with measured ones.